1. Field of the Invention
This invention relates to scroll type fluid apparatuses, and more particularly, to a scroll type supercharger for use with an automotive engine.
2. Description of the Prior Art
Scroll type fluid apparatuses are known in the art and may be designed as either compressors or superchargers. If a high compression ratio is required, the scroll type fluid apparatus is designed as a compressor as disclosed in U.S. Pat. No. 4,477,238 to Terauchi, hereby incorporated by reference. However, compressors, as in the '238 patent, have a low discharge flow rate. If, a high discharge flow rate is required, rather than a high compression ratio, the scroll type fluid apparatus may be designed as a supercharger as disclosed in Japanese Patent Application Publication No. 58-62,301. However, the supercharger has a significantly reduced compression ratio as compared to the compressor disclosed in the '238 patent.
Additionally, the discharge rate of the scroll supercharger is limited due to mechanical limitations on the length of the spiral elements of the scrolls. The length of the spiral element is limited because as the length is increased, the strength of the scrolls is decreased, and the difficulty in machining increases. Superchargers having an increased discharge flow rate in comparison with the supercharger of the '301 application are known, for example, the roots displacement compressor as disclosed in Japanese Utility Model Application Publication No. 62-183,092. However, the compressor of the '092 publication has a much larger exterior dimension than the supercharger shown in the '301 application.
Scroll type superchargers having increased discharge flow rate without suffering the drawback of having an increased exterior dimension are known, as shown in West German Patent Application Publication No. DE 3,141,525-A. The scroll type supercharger disclosed in the '525 application includes an orbiting scroll having a single end plate member from which first and second orbiting spiral elements extend from opposite sides. The orbiting scroll is disposed in a housing which includes two opposite sides, such that third and fourth fixed spiral elements project inwardly from each side. The third spiral element interfits with the first spiral element to define at least one pair of fluid pockets therebetween. Similarly, the fourth spiral element projects from the opposite side of the housing and interfits with the second spiral element to form at least one pair of fluid pockets therebetween.
The drive mechanism includes a crank shaft extending centrally through the housing. Orbital motion is effected by a crank pin disposed about and fixed to the drive shaft, such that the central axis of the crank pin is offset from the central axis of the drive shaft. The crank shaft is centrally disposed through the single plate member which is supported by bearings about the crank pin. Rotational motion of the drive shaft about its central axis, causes rotational motion of the crank pin such that the central axis of the crank pin rotates about the central axis of the drive shaft. Thus, the orbiting scroll orbits within the housing. A rotation prevention means is provided to prevent rotation of the orbiting scroll during orbital motion. A pair of balance weights are attached about the drive shaft, one on either axial end of the crank pin.
In operation, orbital motion of the orbiting scroll causes the fluid pockets to decrease in volume, thus increasing the pressure of the fluid therein. The increasing pressure in the fluid pockets acts equally on both sides of the single plate member, in a direction which is generally parallel to the axis of the crank shaft. Since the pressure on either side of the plate member is generally equal, no net axial force acts on the plate member. Therefore, since no net axial force acts on the plate member, undesirable bending or warping of the plate member is avoided.
However, although the scroll type supercharger as described in the German publication does not suffer from the drawback of bending or warping of the orbiting scroll member, in order to achieve this feature, both the first and second orbiting spiral elements must be formed on opposite sides of a single end plate member. Great difficulty is encountered in manufacturing the orbiting scroll with a sufficient degree of accuracy so as to achieve the necessary relative location of the first spiral element with respect to the second spiral element such that the first and second spiral elements simultaneously interfit with the third and fourth fixed spiral elements, respectively, for efficient operation of the supercharger. Accordingly, due to the difficulty of machining the orbiting scroll, low productivity is obtained with a corresponding high costs of manufacturing in the above type supercharger.